Laboratory studies on the larval growth and development of Nyctiphanes capensis (Euphausiacea)

Larvae of Nyctiphanes capensis Hansen were reared in the laboratoryunder different trophic conditions (i.e., algal, animal andmixed diets) from the second calyptopis stage to the first juvenilestage. It is demonstrated that diet is important in determininggrowth rates and development of the larvae. The highest growthrates were achieved on diets of Artemia nauplii mixed with eitherthe flagellate Tetraselmis or Pseudodiaptomus nauplii. Poorerdietary conditions such as with the diatom Phaeodactylum yieldedslower growth rates where additional moults were needed to completefurcilia development. Under favourable trophic conditions theintermoult period was 4–6 days and was not age dependent.Three dominant pathways of pleopod development were found inhealthy individuals.     

Diel feeding periodicity, daily ration and vertical migration of juvenile Cape hake off the west coast of South Africa

Feeding periodicity, daily ration and vertical migration of juvenile Cape hake Merluccius capensis are investigated from midwater and bottom trawl collections taken during a 42-h period between 29 February and 2 March 1992 at a fixed position off the west coast of South Africa. Feeding of 10-20 cm hake intensified during the night when they ascended into subsurface layers to prey on recruits of anchovy Engraulis capensis. Larger hake remained close to the bottom, were partially cannibalistic and exhibited no diel feeding periodicity. M. capensis appear to migrate vertically and feed asynchronously in midwater, as individuals, and not as a population, returning to the bottom when satiated. Based upon the exponential rate of decline in stomach fullness throughout the day, the evacuation rate by hake <20 cm was estimated as 0.054 h⁻¹; 90% evacuation of anchovy prey required an estimated 43 h. Using the Elliott & Persson and Eggers methods, the daily ration was estimated as 5.51 and 4.15% of wet body weight respectively. The effect of the foraging behaviour of M. capensis on the appropriateness of acoustic sampling for estimates of their abundance is discussed.     

Vortex flow filtration of mammalian and insect cells

The use of vortex flow filtration for harvesting cells or conditioned medium from large scale bioreactors has proven to be an efficient, low shear method of cell concentration and conditioned medium clarification. Several 8–10 L batches of the human histiocytic lymphoma U-937 cell line (ATCC CRL 1593) were concentrated to less than 1 L by vortex flow filtration through a 3.0 m membrane. An aggressive filtration regimen caused a 17% loss of cell viability and a 32% loss of IL-4 receptor binding capacity when compared to a batch centrifuged control. A reduction of the rotor speed from 1500 to 500 RPM and reduction of system back pressure from 10 to 0 PSIG resulted in cell viability and IL-4 binding capacity comparable to the control. Several 10 L batches of baculovirus infected Sf-9 cells were also concentrated to less than 1 L by vortex flow filtration through a 3.0 m membrane. SDS-PAGE analysis of filtrate samples showed that aggressive filtration caused cell damage which led to contamination of the process stream by cellular lysate. When rotor speed was reduced to 500 RPM and system back pressure was reduced to 0 PSIG, the amount of contaminating lysate proteins in filtrate samples was comparable to a batch centrifuged control.     

Cloning and characterisation of the cytochrome c gene of Aspergillus nidulans

The cytochrome c gene (cycA) of the filamentous fungus Aspergillus nidulans has been isolated and sequenced. The gene is present in a single copy per haploid genome and encodes a polypeptide of 112 amino acid residues. The nucleotide sequence of the A. nidulans cycA gene shows 87% identity to the DNA sequence of the Neurospora crassa cytochrome c gene, and approximately 72% identity to the sequence of the Saccharomyces cerevisiae iso-1-cytochrome c gene (CYC1). The S. cerevisiae CYC1 gene was used as a heterologous probe to isolate the homologous gene in A. nidulans. The A. nidulans cytochrome c sequence contains two small introns. One of these is highly conserved in terms of position, but the other has not been reported in any of the cytochrome c genes so far sequenced. Expression of the cycA gene is not affected by glucose repression, but has been shown to be induced approximatly tenfold in the presence of oxygen and three- to fourfold under heatshock conditions.     

Population structure, reproductive biology and maintenance of Euphausia lucens in the southern Benguela Current

This study investigates the population structure and reproductivebiology of the euphausiid Euphausia lucens in relation to temporaland spatial variations in the abiotic and biotic environmentin the St Helena Bay region off the west coast of South Afnca.This is an area of high biological productivity and is importantfor recruitment to the pelagic fishery. Gravid females (stageIV) and young larvae were collected throughout the year, suggestingcontinuous breeding. Spawning was most intense from August toOctober (late winter to early spring) just prior to the onsetof upwelling and an associated increase in phytoplankton. Recruitmentwas high until early summer (August-January) and decreased toa low level throughout autumn and early winter (February-June).The proportion of gravid females increased with distance offshoredespite relatively low chlorophyll a concentrations offshore.Multiple spawning is inferred from the high frequency of gravidfemales in the population. The reproductive strategy and verticaldistribution of all developmental stages of E.lucens is relatedto the current regime of the study site in order to formulatemechanisms most likely to play an important role in maintainingcoastal populations of E.lucens in the southern Benguela Current.     

Burning effects on detritivory and litter decay in Campos grasslands

Disturbances are primary forces creating spatial heterogeneity in ecosystems, and inducing changes on biological communities, abiotic characteristics and ecological processes. Here we focus on the effects of fire disturbance in the decomposition process at subtropical Campos grasslands in South Brazil, where burns are traditionally used to reduce shrub encroachment, and improve forage quality. We experimentally investigated how burns and the changes they produce in grassland habitat conditions affect soil fauna detritivory and surface leaf‐litter decaying patterns over one year. Previously to fire, we found significant correlation of litter decay with plant evenness and detritivory rates in non‐disturbed grasslands. One month after fire grassland patches presented reduced soil fauna densities and surface feeding activity possible because of the mortality caused directly by heating, and/or due to harsh microenvironmental filters to fauna colonization and permanency (e.g. decreased humidity). At 6–7 months after fire however these features did not differ any more from the paired unburned plots. On the other hand, canopy openness accelerated the decaying of leaf‐litter in burned patches by allowing increased action of abiotic factors as solar radiation potentially triggering photodegradation. These effects seemed to last less than one year. Overall, our results bring insights regarding drivers of soil ecological processes at local scales in subtropical grasslands, and suggest that detritivory and litter decay processes are sensitive to fire, but resilient following grassland recovering.